Chitosan production

ABSTRACT

The invention provides a method of producing chitosan using pressures greater than 0 PSIG. The invention also provides fungal chitosan compositions.

CROSS REFERENCE TO RELATED APPLICATIONS

This is the U.S. national stage of PCT/US03/10560 filed Apr. 2, 2003, which claims priority to U.S. provisional application No. 60/369,594, filed Apr. 2, 2002, which is herein incorporated by reference.

FIELD OF THE INVENTION

The invention relates to producing chitosan.

BACKGROUND

Chitosan is a deacetylated form of chitin. Chitin is a polysaccharide that is found in the shells of insects, crustaceans, mollusks, and fungal biomass. Chitosan has been identified as having various uses, for example as a binder in paper making, a component in bandages, and as a wound healing compound.

The quality of chitosan varies with the degree of deacetylation of the N-acetyl groups, molecular weight, purity, manufacturing process, color, clarity, consistency, and uniformity.

SUMMARY

The invention provides a method for producing fungal chitosan from chitin-containing material using greater than 0 PSIG (pounds per square inch gauge). This method allows for the production of chitosan with increased deacetylation levels and increased molecular weight compared to similar processes that do not use increased pressure. Similarly, the invention provides chitosan that has greater purity increased molecular weight, and increased deacetylation compared to processes that do not use increased pressure. Because the invention provides a method for producing high purity fungal chitosan from chitin-containing material it is not necessary to take additional steps to purify the chitosan. However, if the desired product requires utilization of reaction parameters that do not yield high purity it may be desirable to separate the chitosan from the reaction. Separation can be accomplished using any method known in the art, i.e filitration, centrifugation, etc.

Another aspect of the invention provides compositions made by the method.

In yet another aspect the invention provides fungal chitosan compositions that are characterized by their combination of increased molecular weight and increased deacetylation levels, as well as compositions characterized by their combination of increased deacetylation levels, increased molecular weight and increased purity.

FIG. 1 is a graph showing a comparison of the average molecular weight to the percent deacetylation.

FIG. 2 is a graph showing a comparison of the average molecular weight to the percent purity of chitosan.

FIG. 3 is a graph showing a comparison of the percent purity of the chitosan to the percent deacetylation of the chitosan.

DETAILED DESCRIPTION

Fungal Biomass

Chitosan described herein is prepared from chitin contained in fungal biomass. Suitable sources of fungal biomass include, for example, Aspergillus niger, Aspergillus terreus, Aspergillus oryzae, Candida guillermondii, Mucor rouxii, Penicillium chrysogenum, and Penicillium notatum.

Fungal biomass usually has between 5 and 25 percent chitin, and typically from 10 to 20 percent chitin, based upon dry weight of the biomass. Particularly useful sources of fungal biomass are commercial fermentation processes such as those used to make organic acids, such as citric acid.

Caustic

Caustic material can be used either in the reaction directly or in an aqueous solution. Examples of caustic material that can be used in the reaction include, sodium hydroxide, potassium hydroxide, calcium hydroxide, caustic alcohol, or other alkalis. Any concentration of caustic can be used provided that the caustic reacts with the other components of the reaction to yield chitosan. Generally, caustic is used at a concentration from about 5% to about 40% by weight, and more specifically from about 15% to about 30% by weight.

Reaction Conditions

The reaction that causes the production of chitosan from fungal biomass and/or chitin from fungal biomass (hereinafter collectively referred to as chitin-containing material), involves reacting the caustic material with the chitin-containing material at a pressure greater than atmospheric pressure. The temperature, time of reaction, and pressure that are used to form chitosan will vary depending on the desired deacetylation level and the desired molecular weight of the chitosan.

Any temperature that will produce the desired chitosan product can be used. However, temperatures from about 80° C. to about 150° C. and more specifically, temperatures greater than 90° C., 100° C., 115° C., 125° C., 130° C., and 140° C can be used to produce the chitosan.

The reaction can be carried out for any length of time that will produce the desired chitosan product. However, typical reactions times vary from about 1 hour to about 50 hours and more specifically, reaction times greater than 4, 6, 10, 15, 20, 25, and 30 hours are preferred.

Any pressure that is greater than 0 PSIG can be used to produce the chitosan. Generally, pressures greater than 1, 2, 3, 5, 10, 15, or 20 PSIG are used. The pressure can be increased to the theoretical maximum pressure, which depends on the temperature, solubility of the caustic, and the concentration of other reactants in the solution.

Pressure can be applied by using any method known to those of ordinary skill in the art. For example, pressure in the reacting vessel can come from increased vapor pressure due to higher temperatures achieved in a closed vessel, or can come from an external force applied to the vessel contents. Increasing the temperature to 130° C., in a closed vessel containing water, will increase the pressure in that vessel to approximately 15 PSIG. Another way to increase the pressure would be to maintain temperature at a constant level, and apply an outside source of pressure, by reducing the volume of the container, or attaching an outside gas source to raise the pressure to the desired level. This outside source could be an inert gas such as nitrogen, helium or ammonium from a pressurized tank.

Fungal Chitosan

The compositions of the invention are characterized by their combination of high deacetylation levels and high molecular weights. Compositions of the invention can have deacetylation levels greater than 85%, 90%, and 95%. Similarly, compositions of the invention can have molecular weights greater than 80,000, 90,000, 100,000, 150,000, and 175,000.

In other embodiments compositions of the invention can be characterized by their purity level. For example fungal chitosan composition having purity levels of greater than 85%, 90%, and 95% can be obtained.

EXAMPLES

The following examples are provided to demonstrate production of flngal chitosan from a chitin containing material. In the examples depicted, the chitosan was produced under pilot laboratory conditions. However, the invention is also applicable to production of chitosan in large-scale manufacturing operations, particularly where uniform sources of fungal biomass are available.

Example 1 Method of Obtaining and Purifying Chitosan from Fungal Biomass using 20.1% NaOH at Greater than 0 PSIG

29.9 kg of fungal biomass (Aspergillus niger) at 17.14% dry solids, 21 liters of 50% NaOH, and 18 liters of water were added to a pressure reactor which was made using materials available on site. However, commercial models such as, for example, the Miniclave Pressure Reactor from CTP Corporation, Northport, N.Y., can also be used to give the results provided herein. This resulted in a final ratio in the mixture of 6.0% dry biomass, 20.1% NaOH, and 73.9% water. This alkali biomass solution was heated using a steam coil to approximately 130° C. and held in the sealed reactor for 28 hours. Since this was above the boiling point of 20% caustic (109° C.), 14-16 PSIG pressure was contained in the reactor, as well as the ammonia and other gases released in the associated reactions.

Samples were taken periodically. The samples were filtered and washed with water to remove the NaOH, salts and other soluble by-products. The filtered solids contained the chitosan-containing material, made up primarily of chitosan and glucans. The chitosan was then separated from the glucans by dissolving the filtered solids in acetic acid (pH 4.0), and centrifuging to separate the insoluble glucans from the soluble chitosan.

The amount of chitosan was measured and the percent chitosan in the filtered solids was calculated to provide a % purity on a dry weight basis. The average molecular weight of the chitosan was measured by a size exclusion column (SEC) on chitosan that had been separated from the chitosan containing-material by acidifying with acetic acid and centrifugation.

First derivative ultraviolet spectrophotometry was used for measuring the degree of deacetylation of chitosan was first derivative ultraviolet spectrophotometry. This was described by Riccardo A. A. Muzzarelli and Roberto Rocchetti, Determination of the Degree of Acetylation of Chitosans by First Derivative Ultraviolet Spectrophotometry, Carbohydrate Polymers, 5:461-472, 1985.

The results of this example are in Table 1.

Example 2 Method of Obtaining and Purifying Chitosan from Fungal Biomass using 12.8% NaOH at Greater than 0 PSIG

40.8 kg of fungal biomass (Aspergillus niger) at 13.68% dry solids, 11 liters of 50% NaOH, and 12 liters of water were added to a pressure reactor. This gave a final ratio in the mixture of 8.0% dry biomass, 12.8% NaOH, and 79.9% water. This alkali biomass solution was heated using a steam coil to approximately 130° C. and held in the sealed reactor for 45 hours. Since this was above the boiling point of 12% caustic (104° C.), 18-20 PSIG pressure was contained in the reactor, as well as the ammonia and other gases released in the associated reactions.

Samples were taken periodically. The samples were filtered and washed with water to remove the NaOH, salts and other soluble by-products. The filtered solids contained the chitosan-containing material, made up primarily of chitosan and glucans. The chitosan was then separated from the glucans by dissolving the filtered solids in acetic acid (pH 4.0), and centrifuging the insoluble glucans from the soluble chitosan.

Measurements were made in a similar manner to those described in Example 1.

The results of this Example are in Table 2.

Example 3 Method of Obtaining and Purifying Chitosan from Fungal Biomass using 30.1% NaOH at Greater than 0 PSIG

Chitosan was obtained and purified from Aspergillus niger using 30.1% NaOH. Other than a different caustic level, the conditions and processing steps are similar to those used in Example 2.

The results of this Example are shown in Table 3.

Example 4 Method of Obtaining and Purifying Chitosan from Fungal Biomass using 24.9% NaOH at 0 PSIG

208.6 kg Aspergillus Niger mycelium of which 18% was dry matter was mixed with 135 L of 50% NaOH to make a mixture that contained 24.9% NaOH and 8.9% solids. The mixture was heated to 110° C. for the time periods indicated in Table 4, below. Analysis of products are reported in Table 4.

Example 5 Method of Obtaining and Purifying Chitosan from Fungal Biomass using 30% NaOH at 0 PSIG

254 kg Aspergillus Niger mycelium of which 18% was dry matter was mixed with 250 L of 50% NaOH to make a mixture that contained 30% and 7% solids. The mixture was heated to 118° C. for the time periods indicated in Table 5, below. Analysis of products are reported in Table 5.

TABLE 1 Average Average 20.1% NaOH Molecular Molecular Chitosan Time Temp Pressure Weight of Number of % DA of Purity in (hr) (C.) (PSIG) Chitosan Chitosan Chitosan dry cake 4 130 14 169,104 48,350 79 43.0 12 132 14 232,964 45,637 82 82.8 16 130 16 201,681 41,401 85 91.4 20 132 14 178,736 37,254 86 92.1 24 129 14 142,814 33,144 88 97.1 28 130 14 122,975 28,540 89 98.4 PSIG* pounds per square inch gauge Cake* refers to the dry solids remaining after the reaction % DA* refers to percent deacetylation

TABLE 2 Average Average 12.8% NaOH Molecular Molecular Chitosan Time Temp Pressure Weight of Number of % DA of Purity in (hr) (C.) (PSIG) Chitosan Chitosan Chitosan dry cake 6 130 14 147,574 38,236 83 50.5 12 128 13 226,316 38,349 82 80.6 15 130 15 258,933 38,428 83 81.9 18 128 15 210,449 34,844 84 80.3 24 128 14 203,543 33,856 87 84.5 30 130 15 150,629 26,669 89 90.3 40 130 15 101,464 23,253 92 95.0 42 130 15 103,143 23,624 93 97.9 45 130 15 103,143 23,624 93 97.9

TABLE 3 Average Average 30.1% NaOH Molecular Molecular Chitosan Time Temp Pressure Weight of Number of % DA of Purity in (hr) (C.) (PSIG) Chitosan Chitosan Chitosan dry cake 2 131 14 206,647 61,876 89 53.0 4 135 11 176,844 50,253 90 76.9 6 133 10 152,997 42,720 91 80.2 8 133 10 134,026 38,885 92 87.8 10 132 13 115,210 34,949 93 85.5 12 132 11 107,080 32,099 94 89.7 14 132 10 100,386 29,954 93 94.6 16 132 10  89,452 29,416 94 96.9

TABLE 4 0 PSIG 24.9% NaOH Average Chitosan Molecular Average Purity Time Temp Weight of Molecular Number % DA of in dry (hr) (C.) Chitosan of Chitosan Chitosan cake 3 109 106,615 44,690 73.8 15.3% 4 108 101,681 43,523 81.1 22.7% 6 108  99,004 42,855 82.4 27.1% 7 108  99,850 40,977 85.2 29.9% 8 112  91,112 39,815 84.9 35.9% 24 111  77,626 32,463 93.2 39.0%

TABLE 5 0 PSIG 30% NaOH Average Average Molecular Molecular Chitosan Weight of Number of % DA of Purity in Time (hr) Temp (C.) Chitosan Chitosan Chitosan dry cake 2 85 157770 81506 71.8 19.5% 4 105 144843 70204 79.7 25.8% 7 115 123054 58453 89.0 33.7% 12 119 95370 42371 90.4 57.9% 14 119 88609 39735 91.0 64.0% 16 117 83685 37011 92.0 65.6% 18 114 83104 35751 91.0 72.6% 20 115 80494 35611 91.5 74.2% 22 115 75438 32930 92.3 74.4% 24 117 74664 31919 92.7 75.4% 26 115 72383 31153 93.4 78.7%

The results provided above show that at pressures greater than 0 PSIG the molecular weight of chitosan is greater at a specific deacetylation level when compared with chitosan made at 0 PSIG at the same deacetylation level. Furthermore, it is expected that by maintaining constant pressure on the reaction, greater temperatures can be used while not depolymerizing the chitosan.

Graph 1 provided below presents a comparison of the average molecular weight to the percent deacetylation from Tables 1 through 5 above. The open symbols represent data collected at 0 PSIG, and the solid symbols represent data collected at pressures greater than 0 PSIG.

The results provided above also show that at pressures greater than 0 PSIG the molecular weight of chitosan is greater at a specific purity level when compared with chitosan made at 0 PSIG at the same purity level.

Graph 2 provided below presents a comparison of the average molecular weight to the percent purity of the chitosan from Tables 1 through 5 above. The open symbols represent data collected at 0 PSIG, and the solid symbols represent data collected a pressures greater than 0 PSIG.

The results provided above also show that at pressures greater than 0 PSIG the average molecular weight is greater at higher percent purity of chitosan level when compared with chitosan made at 0 PSIG at the same purity level.

Graph 3 provided below presents a comparison of the percent purity of the chitosan to the percent deacetylation of the chitosan from Tables 1 through 5 above. The open symbols represent data collected at 0 PSIG, and the solid symbols represent data collected a pressures greater than 0 PSIG.

The results provided above also show that at pressures greater than 0 PSIG the percent purity of chitosan is greater at a specific percent deacetylation level when compared with chitosan made at 0 PSIG at the same purity level.

Having illustrated and described the principles of the invention in multiple embodiments and examples, it should be apparent to those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. We claim all modifications coming within the spirit and scope of the following claims. 

1. A method for producing chitosan from fungal biomass, comprising: reacting the fungal biomass with a caustic at a pressure greater than 0 PSIG for at least 4 hours, thereby producing chitosan, wherein the average molecular weight of the chitosan is greater than 80,000 and less than about 258,933.
 2. The method according to claim 1, further comprising separating the chitosan from the reaction.
 3. The method according to claim 1, wherein the pressure is greater than 5 psig.
 4. The method according to claim 1, wherein the pressure is greater than 10 psig.
 5. The method according to claim 1, wherein the temperature is greater than 115° C.
 6. The method according to claim 1, wherein the temperature is greater than 125° C.
 7. The method according to claim 1, wherein the reaction occurs for greater than 15 hours.
 8. The method according to claim 1, wherein the caustic is 5% to 40% by weight percent.
 9. The method according to claim 1, wherein the caustic is 15% to 30% by weight percent.
 10. The method according to claim 1, wherein the reaction occurs for greater than 6 hours.
 11. The method according to claim 1, wherein the reaction occurs for greater than 10 hours.
 12. The method according to claim 1, wherein the pressure is greater than 15 PSIG.
 13. The method according to claim 1, wherein the pressure is greater than 20 PSIG.
 14. A method for producing chitosan from fungal biomass, comprising: reacting the fungal biomass with a caustic at a pressure greater than 0 PSIG at a temperature greater than 125° C. for at least 12 hours, thereby producing chitosan, wherein the average molecular weight of the chitosan is greater than 80,000 and less than about 258,933.
 15. The method according to claim 1, wherein the fungal biomass is Aspergillus biomass. 